1. Field of the Invention
The present invention relates generally to oscillator circuits for providing a waveform of a predetermined frequency. More particularly, the invention relates to an oscillator circuit that minimizes input power requirements having a continuous pulse output.
2. Discussion
With the current growth in electrical and electronic technology, there is a growing interest in broadening the maintenance and service functions of various systems. One of the more promising areas for increasing system monitoring capability is automotive ignition off systems.
Numerous functions in an automobile are monitored by on-vehicle systems when the ignition is off. Examples of such functions include, door ajar detection and alarm, remote keyless entry, local door lock/unlock, and anti-theft alarm systems. The availability of these functions provide consumers with enhanced convenience and comfort, however in return there is an increased risk that the vehicle battery will not retain sufficient energy to start the vehicle because of the ignition off draw (IOD) required to power the monitor circuits. Due to the continuous power drawn from the battery there is a limited period of time that the vehicle can remain idle before the battery stored charge is depleted.
In general, IOD monitor circuits comprise sensors to acquire data, analog-to-digital conversion circuitry, microprocessors to manipulate the digital data, and oscillators to drive the microprocessors. In IOD monitor circuits the oscillator consumes a significant portion of the power that drives each circuit. Generally, an oscillator is comprised of a linear portion that generates a sinusoidal waveform at a predetermined frequency and a buffer amplifier that converts the sinusoidal signal to a square-wave output which is suitable for driving a microprocessor. The output drive stage of the linear portion of the oscillator consumes the majority of the power within the circuit. The drive stage is typically a push-pull Class AB amplifier configuration in which the current draw is directly related to the voltage applied. Powering the entire oscillator from the same voltage level results in significant power consumption within the linear stage of the circuit, thereby substantially reducing the period of time a vehicle may be left idle before the battery dies. While conventional oscillator circuit configurations can be used to drive microprocessors, they have not proven capable of providing a clock signal without substantial power consumption.
Therefore, it is desirable to reduce the IOD of automotive electrical circuits by reducing the power consumption of the oscillator circuits. Powering the linear portion of the oscillator circuit from a lower voltage level than the remainder of the circuit minimizes the circuit power consumption.
It is another object of the present invention to provide a fast start-up capability so that the oscillator can be maintained in a low-power sleep mode, thereby minimizing power consumption during periods of time when the particular monitor circuit is not required.
It is also another object of the present invention to use a common source voltage to power the oscillator and the remainder of the circuit. Employing a common voltage source minimizes the cost and complexity of the overall system.
Further, it is another object of the present invention to employ standard low-cost devices for the oscillator circuit.